Posted
by
samzenpus
on Thursday November 05, 2015 @07:20PM
from the solving-a-mystery dept.

StartsWithABang writes: If you came to the Solar System some 500 million years after its formation, you would've found two world with oceans of liquid water, continents and all the conditions we know of for life to begin thriving: Earth and Mars. But unlike our own world, Mars' organic history was cut short when it lost its atmosphere and became a barren, desert wasteland. While we had some pretty compelling theories as to how this happened, it was only with the advent of the Maven mission and its first science results that we discovered exactly how, how fast and when Mars lost its atmosphere. One cool discovery: aurorae appear diffuse and all over the entire night sky on Mars!

The summary is missing important information. As TFA discusses, the primary issue was (as already strongly suspected) the loss of the magnetic field around Mars. With only a very weak magnetic field nothing protected the planet's atmosphere from the solar wind which blasted the atmosphere away over a time span probably in the hundreds of millions of years. This last result, the slow loss of the atmosphere is a genuinely novel and important discovery because as TFA discusses this makes it more plausible that if there was life on Mars that it would have had time to evolve to survive the gradually harsher environment. The research also suggests that Mars will become completely airless in around 2 billion years.

Mars, being half the diameter of Earth, has a higher surface to volume ratio. Thus, it cooled faster. Presumably the liquid core froze, or at least, enough of it froze to stop the dynamo of molten metal that creates the magnetic field

Mercury gets plenty of heat from the sun and has an absolutely huge metal core.
Not sure about Venus, though. Maybe it has a smaller core than you'd expect for a planet its size? It's difficult to tell, since its atmosphere has a nasty habit of melting all our probes.

Mercury's ROTATION is in resonant synchrony with it's ORBIT around the Sun, but that doesn't change the tidal forces themselves. It changes the change of tidal forces around the orbit, and therefore the work done on the planet by those forces. So tidal heating is minor.

What heats Io (and other Jovian and Saturnian satellites) is the change of forces on on the planet between those from Jupiter (Saturn) and the forces from the other satellites.

My apologies, seems that Mercury has the largest orbital eccentricity of the planets and therefore 17 times higher tides then the Earth. Still sounds like the magnetic field is caused by the extra large core which is probably still molten from formation.

Venus has a higher average temperature than any other planet - the clouds do a good job at distributing the heat fairly evenly about the planet regardless of the latitude, season, or whether it is day or night.

Mercury has a lower average because there's nothing holding heat in on the night side. It does, however, hold the record for the greatest temperature difference in the solar system, between the day and night halves.

Actually judging by the amount of sulfur and potassium in the crust, it was not involved in a giant collision. leading theory is that during formation the solar wind drove away the lighter materials with another theory that it was so heated that it had a rock vapor atmosphere which the solar wind drove away.

Probes don't matter for getting the gross composition of the planet. Since the 1770s (when we got the scale of the solar System from the successful observation of a transit of Venus, and returned the data and did the calculations) we've known that Venus weigh about 5*10^24 kg, has a volume of about 9*10^11 km^3 (I'm being deliberately vague, as our precision has improved over the centuries), for a density of 5.3 tonnes/ m^3.

Bulk rocks have density between 2.5 and 3.1. With compression in the depths that ge

Well, if you consider the longest a species of life on Earth has existed (which is about 200 million years I think) against time time frames being given for cores cooling and atmospheres being stripped... "how long do *we* have?" is the wrong question.

Gravity. Venus has about 0.8 the mass of the Earth. Mars has about 0.1 of the mass. That's a big difference. Without that extra mass, Mars doesn't have the gravity to hold in the atmosphere, so the solar wind is strong enough to strip it away. On Venus, there's plenty of mass to generate gravity which keeps the atmosphere in place with more force than the solar wind has to strip it. On Earth, there's even more gravity plus a magnetic shield that negates the solar wind completely.

Trouble is getting there in the first place won't be.It is far more difficult (and costs a LOT more energy) to send a rocket to the inner planets than to an outer planet. The reasons are a bit complicated for a slashdot post (it's about how much orbital velocity you need around the sun in a smaller orbit and then to get into planetary orbit you have to slow down by a lot more).

It's possible and we've sent probes to venus but they used a lot more fuel than the same size probe would need to Mars despite Mars

(They mention this in the video but it still seems important to state) Venus is much more inhabitable than Mars is. The biggest issue at the moment is the fact that Venus's surface temperature is above 450 C. We currently know how to make a planet warmer over time, but we don't know how to make a planet that much cooler for multiple reasons. Partially because of the fact that with a sulfuric atmosphere and that temperature it becomes very difficult to even get any machines there for colonization.

Venus is actually a fairly interesting prospect for colonization. You obviously don't go down to the surface with its lead-melting temperatures. However, about 50km from the surface you have temperatures a bit above freezing, the atmospheric pressure of roughly one atmosphere, and gravity that's very near Earth's. It's about the most earth-like place in the solar system that's not on Earth itself. The atmosphere is mostly CO2, which is a dense gas, so a balloon filled with breathable air would float. Y

Without following the clickbait, there's a good chance that you're correct.

But what's the point about the cost of sending people there? Apart from the first few colonists - a few thousand - they'll breed their own inhabitants. why would they want poor foreign immigrants from a polluted or nearly uninhabitable planet like Earth will be in the thousands of years that the project would take.

Or... were people thinking of dreams about the future being a substitute for dealing with current problems?

No it isn't. The summary is providing just enough information to force you to go to the site for the answer. Look at the author. He didn't miss anything, he calculated the required amount of clickbaitness.

But what's the point in doing all the hard work to terraform Mars when there is nothing that can be done to stop this? The planet is dead unless we can increase the mass and magnetic fields, two things we don't have the science to do, nor will have in any remotely near timespan.

That's about a kiloton of coal every four months to just replace the current carbon that's being lost. To actually make a dent in the planet's carbon supply, it would be necessary to add more than that. Good luck finding the fuel to transport that, and the people who would be happy to see so much carbon leave Earth.

The article says it would last for a while if we could, so...back of the envelope with probably horribly wrong numbers. Martian atmospheric density at the surface is 0.020 kg/m^3, human survival limit is something like 0.6 kg/m^3, so we need to add 29x current martian atmosphere to be long-term human survivable without a mask (for children and older, babies would still need higher pressure). NASA puts current atmospheric mass at 2.5e16kg, so we need to add 7.25e17kg. If we wanted to accomplish that task over a thousand years, or roughly 3.15e10 seconds, we would need to produce about 2.30e7kg of atmosphere every second for the duration. (At that speed, the loss rate of Mars's atmosphere due to solar wind is absolutely negligible.)

Martian surface area is 1.44e14m^2, which means we'd need to pull ~5,000 kg of atmosphere out of every single square meter of the planet if we don't have some other source. I don't know what density or composition Martian rock is, but rock in general is about 2.5g/cm^3, or 2500kg/m^3. So you might need to dig several meters into the ground to get what you're after, and expend one hell of a lot of energy to crack the oxygen out of it, but it's not like you'd need to dig a whole mile down across the whole planet or anything.

...new idea. If you already have the crazy tech necessary to do all that, just have your robots fabricate enclosed colony space instead. Mine, smelt, build roof. Yeah it's still ridiculous future technology, but if all you want is to make the place livable, it's a lot faster if you just make a bunch of buildings. Hell, in the amount of time it would take to crack all those atmospheric gases, you could have your crazy future robots just build an entire planet-covering roof for an enormous habitation space. It would take less work.

Anti-Mars people seem to miss that point. If you are on Mars surface, Mars is shielding you from half the constant radiation. Create buildings with a thick roof on top and big windows on the side, like most apartment and office buildings, and you are about as protected as on Earth.

Or we relocate Callisto, as in arrange a collision between Mars and Callisto. If that isn't enough energy to remelt Mar's core, then add Mercury. Or probably bang Mercury and Mars together first, then drop in Callisto so you don't lose the water that makes up Callisto. That might get you a habitable planet once the crust hardens up again.

Heat mars....perhaps covering it in dark dust at the polar caps, put some machines there to pump out CFCs...global warming will cause sublimation of dry ice into carbon dioxide, a green house gas...planet heats more, more is sublimated, etc...hopefully get a positive feedback cycle going...

I believe the normal science fiction solution is throwing comets at it. The comets can add water and various gases (although ammonia and methane probably aren't what you want for a liveable atmosphere) along with various organics.

I'm not sure it would do us a lot of good, but it might give Mars a chance to develop life of its own, especially if seeded with simple life from Earth.

Honestly, If we're going that far, I'd say a better target is Venus. Venus has no water. One of the theories for why Venus lack

Submission claims that for the first 1/2 billion years there were 2 planets with water and air. What about Venus?Venus was also possibly inhabitable for the first part of its life, perhaps billions of years, until the Sun got warm enough to boil the Venusian oceans and created a runaway greenhouse affect.Same thing is predicted for the Earth as the Sun continues to heat up (due to having a higher percentage of helium with time and therefore higher density) perhaps in as soon as 500 million years.